High Wind in California, June 28, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
252 PM PDT Sun Jun 28 2020

.SYNOPSIS...Strong winds will spread over the region today and
tonight resulting in a significant fire weather risk as well as
other wind impacts, especially for higher terrain areas. This
windy event should conclude late tonight and allow for a cold
front to bring much cooler temperatures to begin the upcoming week
then a gradual warm up expected moving into the holiday weekend
and an increasing chance for some isolated thunderstorms for
northwest Arizona.

&&

.AFTERNOON UPDATE...
All in all, the forecast has performed pretty well looking at hourly
winds and observations. As mentioned on the morning discussion, we
continue to see a secondary surge of winds, specifically downslope
potential for the Spring Mountains, San Bern higher terrain, and
lingering winds on the eastern Sierra south of Olancha that look to
persist a few hours beyond the original wind advisory. As such,
opted to extend the entire NPW to capture these areas and allow for
strategic cancellation if needed. However, not confident that
potential wind impacts won't linger beyond 6Z.

Additionally, KLAS winds have periodically touched Airport Weather
Warning criteria and do not anticipate these winds to subside much
through the next several hours, thus opted to issue this as well for
McCarran.

Lastly, latest webcams and satellite obs confirm a new, rather
large looking fire was seen near Kyle Canyon in the last 30 minutes.
So wind and fire concerns continue through the afternoon. No other
major changes expected in the near term.

.SHORT TERM...through Monday.
All eyes are on wind potential today and what impacts that may
bring to the region. Some fine tuning of wind grids this morning
did not result in much overall change in the expectations for
today.

One consideration was a possible upgrade to a high wind warning
for northern zones such as Lincoln/Esmeralda/Nye counties (zones
014/015). While there is some support, namely from the GFS LAMP
and GFS based outcomes today for sustained winds reaching 40 mph
and/or gusts over 58 mph, the majority of guidance is below these
thresholds. NBM has consistently kept gust potential below these
criteria as well as HRRR/HRRRX/RAP and other hi res guidance so
feel confident with the strongly worded NPW currently in place. We
did however move the start time up to begin this morning as some
gusts were already exceeding 40 mph and some dust impacts
impacting the valley.

Two main impacts will be of focus today in regards to the
aforementioned wind. First, wildfire potential, which has been
mentioned for the last several days, but is of particular concern
with two large fires in Lincoln county. Both GOES-W meso-sectors
are focused on the southwest today to help monitor these fires.

Second is dust potential. Already this morning, the Jean dry lake
bed erupted into a significant plume of dust that reduced
visibility briefly for KLAS/KHND and the eastern Valley. This
should continue to be the case periodically throughout the day
today as winds continue to increase through the afternoon. Will be
keeping a close eye on other dust sources across the Great Basin
for potential need for dust storm warnings. Did increase the dust
wording in the Wx grids as well.

Contrary to indications yesterday, there may be a need to extend
some of the wind products after 06Z tonight looking at the latest
wind trends. This will be highly dependent on frontal timing and
the magnitude of post frontal winds though. For now, left this
unchanged but will continue to look at this through the afternoon.
May leave this as a short-fuse decision tonight nonetheless.

Moving into Monday, wind potential decreases substantially, with
elevated winds remaining for eastern Mohave County, enough to
result in borderline RFW criteria. Otherwise, the main weather
talking point for Monday will be the much cooler temperatures that
continue to trend downward with latest NBM guidance. As of now,
KLAS looks like it may not even reach 90 degrees.

.LONG TERM...Tuesday through the Weekend.
A period of below normal temperatures will be welcome through the
first half of the week but this trend will not hang around for
too long. Temperatures should respond to building heights and a
transition to southwest flow over the Southwest. A quasi-
monsoonal-like pattern attempts to set up with a weak high
positioned over the southern US Thursday and shifting west over
central NM Friday. This in phase with a broad low over the Pacific
Northwest would set the stage for building moisture depending on
how these features orient themselves. Late week ensemble cluster
do show these details are not yet high confidence, but PWAT values
do markedly increase late week up the Colorado River Valley and
east. NBM still keeps PoPs below mentionable values Thursday and
Friday but decided to increase PoPs to at least slight chance for
these two days for Mohave County given the synoptic set up, modest
instability and PWAT ranges from 0.75 to 1.1" per GEFS/EC ensemble
members. After Friday, details are even less clear but the ridge
continues to slowly creep westward and weaken further which should
push PoP potential more into eastern Arizona and New Mexico.

&&

.FIRE WEATHER...Southwest winds will continue to increase across
the entire region with gusts 35 to 55 mph expected through the
evening. Gusts over 60 mph are likely in the Spring Mountains and
eastern Sierra slopes. These strong winds plus very low relative
humidity this afternoon will result in widespread critical fire
weather conditions across the region. Winds lessen late tonight
and Monday, but still remain elevated, especially across northwest
Arizona. Fire weather concerns diminish due to much lower winds
through much of the week after Monday.

&&

.AVIATION...For McCarran...Strong, south-southwest winds will be
present for much of the day. Dust has been an issue this morning
which briefly dropped vsbys to 2 1/2 miles at the terminal.
Conditions have improved over the last hour. However, there is
potential for brief vsby drops to 2-5 miles this afternoon but
prevailing conditions should be VFR. Peak winds are expected
between 20z and 03z at speeds of 30 knots gusting 40 knots.
However, there could be a second push of strong winds this evening
which would allow these winds to linger through around midnight.
This second push has the potential to be stronger and winds could
reach AWW criteria some time between 03z-08z with speeds of around
35 knots gusting 45-50 knots. Not high enough confidence in this
occurrence to add into the TAF at this time but will continue to
monitor. Late tonight into early tomorrow morning winds will be on
a decreasing trend. A cold front is expected to move through the
valley tomorrow morning between 15z-17z which will shift winds to
the northwest with speeds of around 10 knots gusting 15-20 knots.
Lighter winds expected on Monday.

For the rest of southern Nevada, northwest Arizona and southeast
California...Strong west to southwest winds will continue into this
evening for most areas and even into late tonight for portions of
the Mojave Desert and Clark County. Widespread wind speeds of 25-35
knots gusting 35-45 knots are expected. Strong winds coming off the
Sierra into the Owens Valley this afternoon could even gust as high
as 55-65 knots. High winds will also cause an issue with lowering
vsbys in blowing dust. The Las Vegas valley terminals as well as
KDAG are the most likely to see potential drops to 2-5 miles this
afternoon. A cold front will work its way southward today through
the southern Great Basin and Inyo County; reaching southern Nevada
Monday morning which will turn winds to the north/northwest and
continue gusty winds around 10-20 knots gusting 20-25 knots.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

DISCUSSION...TB3
AVIATION...Guillet

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